Biodegradable plastic material and a method for its manufacture

ABSTRACT

A process of preparing biodegradable plastics material comprising 1) mixing a stabilizer such as an amide or metal salt with a partially hydrolyzed, water-soluble polyvinyl alcohol (PVA) copolymer, 2) adding a plasticizer to the mixture, 3) mixing said materials in the temperature range of between 106 and 140 C. and 4) compounding the blend by known processes.

The present invention relates to a biodegradable plastics material andto a method for its manufacture. In particular, the invention relates toa biodegradable plastics material comprising apolyvinylacetate/polyvinylalcohol copolymer.

Commercially available biodegradable plastics do not fully degrade inthe environment and retain a high degree of toxicity when partiallydegraded. Furthermore, such materials are expansive and generally onlyused for niche markets.

The use of polyvinylacetate/polyvinylalcohol (PVA) copolymers for themanufacture of biodegradable plastics materials is described inWO92/01556. By layering or surrounding PVA which is water soluble at 20°C. with a thin layer of a PVA which is water insoluble at 20° C., anarticle which is protected from dissolution by water until itswaterproofing, insoluble layer is breached may be manufactured. ThePVA's are co-extruded as a laminate or may be moulded, with or withoutan intervening filler layer. Water soluble PVA dissolves readily inwater and is broken down in the environment within a relatively shorttime to carbon dioxide and water.

The Hoescht AG Resins specialty print (1991), "Plastic Films Formed FromPolyvinyl Alcohol" by Albrecht Harricus et al, discloses that in orderto process PVA plastics material on standard processing apparatus suchas profile extruding machines, blown film extruders or injectionmoulding machines, undesirable thermal decomposition of the productsoccurs at temperatures above 150° C. and must be prevented by externalplasticising of granular plastics material. The plastics material isplasticized by mixing with a suitable plasticizer for 15-30 mins. at atemperature of up to 110° C. This plasticized PVA can be injectionmoulded and extruded under the following conditions: heating thematerial to a temperature in the range 145-190° C. and at an injectionpressure of 100-130 bar.

While PVA is known as a biodegradable material, its use in themanufacture of plastic articles has up to now been limited as it istechnically difficult to work with this material and to produce anacceptable product, therefore it is costly and commerciallyunsuccessful.

The present invention seeks to provide an improved plastics materialcomprising a PVA copolymer which can readily be worked by knownprocesses such as blow moulding, injection moulding, cast extrusion,etc. and which is suitable for the manufacture of biodegradablearticles.

The term PVA as used herein refers to a polyvinylacetate polymer whichhas been partially hydrolysed to convert a proportion of the acetategroups to the corresponding alcohol. Therefore, the term refers to apolyvinylacetate/polyvinylalcohol copolymer. The solubility of the PVAis dependent, inter alia, on the degree to which the PVA is hydrolysed."Cold soluble" PVA denotes a copolymer which is generally referred to as"partially hydrolyzed" polyvinylacetate. Typically, the partiallyhydrolyzed copolymer comprises 70 to 85 wt % of the alcohol, with theremainder comprising residual acetate, and this material is soluble in"cold" water. It is generally readily soluble in water at 20° C. Furtherhydrolysis of the PVA to levels at which the alcohol comprises about 96mol % or greater (usually referred to as "fully hydrolyzed"polyvinylalcohol, results in a marked decrease in solubility. While thefully hydrolyzed polymer is usually thought of as insoluble, it is infact soluble in water at a temperature of about 50° C. or greater. Suchmaterial is referred to herein as "hot soluble" PVA. Both hot and coldsoluble PVA's, once dissolved, are fully biodegradable in nature to CO₂and H₂ O. The undegraded copolymers and their partially degradedderivatives are non-toxic.

The present invention provides a method of manufacturing a biodegradableplastics material comprising mixing partially hydrolysed, water solublepolyvinyl alcohol (PVA) co-polymer with a plasticizer and stabiliser ata temperature in the range of between 106 to 140° C., whereby theresultant material can readily be worked by known processes and issuitable for the manufacture of water soluble and biodegradablearticles.

The method may comprise the following steps:

a. mixing the stabiliser with the PVA; and

b. adding the plasticiser to the mixture of stabiliser and PVA andmixing at a temperature between 106 to 140° C.

After the mixing stage, the method may include the steps of compoundingand pelletising the resultant product to produce a useable, commercialpellet wherein the compounding is carried out at a temperature in therange 195-225° C.

The method may include processing the plastics material further by blowmoulding, cast extrusion, injection moulding or any other suitable typeof process currently in use.

The mixing stage may include mixing PVA and stabiliser are mixed in aforced action blender.

The stabiliser may be included in an amount in the range of 4 to 6% w/w(weight of stearamide to weight of PVA) and the plasticiser is includedin an amount in the range of 3 to 15% w/w (weight of plasticiser toweight of PVA).

The stabiliser may stearamide or a stearate and the plasticiser maycomprise glycerol or glycerine solution or soya bean oil.

The mixing stage may be carried out at a temperature in the range of 123to 129° C.

The method may include the step of applying a waterproofing agent to atleast a portion of the surface of the plastics material so that at leasta portion of the material is rendered resistant to water to preventpremature dissolution of the product on contact with water.

The waterproofing agent may be phenoxy resin.

The invention also provides a fully or substantially fully biodegradablearticle produced by the method of the invention.

According to the invention, the addition of a stabiliser to the PVAfeedstock during compounding of the plastics material results in aproduct which can readily be worked into a product by any of thecommonly used methods. The PVA feedstock may be cold or hot soluble,partially hydrolysed PVA which is 70-85 wt % polyvinyl alcohol. A broadrange of polymer molecular weights are suitable for use, depending onthe desired characteristics of the final product. Generally, molecularweights in the range of 20,000 d to 90,000 d are usable. Plastics madefrom PVA's falling into the lower part of this range will be softer andpliable, and will be suitable for making relatively flimsy films.Selection of PVA's from the upper end of the range will allow muchharder plastics to be made, for example for making articles such asbottles, moulds, bowls, etc. The preferred molecular weight range isfrom about 50,000 d to about 60,000 d, degree of hydrolysis 76.7-79.3mol %. PVA's in this range, when compounded as described herein, mayreadily be extruded to give good quality product.

The most preferred stabiliser for use in the manufacture of the plasticsmaterial is stearamide (octadecanamide), which is a fully biodegradablesubstance. Alternatively stearates such as zinc stearate can also beused. Stearamide is added in the range of between about 4 to 6 wt %,with 5 wt % being preferred.

A plasticiser is also added and preferably this will also be abiodegradable substance. Typically, the plasticiser will be glycerol orglycerine and will be present in the range of between about 3 to 15 wt%, preferably 5 to 10 wt % and optimally about 5 wt %. The stearamideand glycerol in combination provide and excellentstabilising/plasticising effect in the plastics material. The rigidityof the plastics product can be controlled by varying the amount ofglycerol and stearamide added, the product becoming softer and morepliable as the weight % of stearamide and/or glycerol is increased.

Other additives, well known in the art, may also be used in compoundingthe plastics material according to the invention. Such additives mayinclude colouring compounds and fillers.

The plastics material may be compounded by any suitable means known inthe art. Most preferably, the PVA feedstock in the form of powder orgranules is mixed with the stearamide, glycerol and optional otheringredients in a forced action blender. However achieved, the mixingwill be done at an elevated temperature of between 106 to 140° C.,preferably between 123° C. and 129° C. when film will be blownsubsequently, and optimally about 125° C. After mixing, the plasticsmaterial may be pelleted or otherwise prepared, ready for forming into adesired article by extrusion, moulding or otherwise.

The article prepared in this way will be fully or almost fullybiodegradable. When it is to be discarded to waste, it need only bebrought into contact with water, either cold or hot, depending on thePVA feedstock chosen, to cause it to dissolve. The dissolved PVA willthen be fully biodegradable within about 28 days to CO₂ and H₂ O.Likewise, the biodegradable additives in the plastics material willdegrade. The PVA in itself is non-toxic and therefore poses noenvironmental hazard during the time during which it is beingbiodegraded.

Clearly, the plastics material described above is suitable only for themanufacture of articles which do not, or are unlikely to, come intocontact with water during their normal usable life. According to anotheraspect of the invention, a PVA plastics articles which is at leastpartially waterproof, water resistant or hydrophobic is provided. Waterresistance will be required in any article which during its normalstorage or use, is in contact with an aqueous environment or a humidenvironment. Those surfaces of the article which are exposed to theaqueous or humid environment need to be protected from that environmentuntil such time as the article is to be discarded to waste. Examples ofsuch articles include, without limitation, plastic bags, sachets, sacks,wrappers, packaging and the like, films, containers including bottles,jars, beakers, pots and the like and liners including sanitary productssuch as napkins, nappy liners and the like. Many other applications willsuggest themselves to the skilled person. In some cases, all surfaces ofthe article will require to be rendered waterproof while in other cases,only a portion of the article need be so treated. However waterproofed,the article will easily be disposed of after use. In the case where onlya portion of the article has been made water resistant, contacting theuntreated portion of the article with water will cause the article as awhole to dissolve. Where all exposed surfaces of the article have beenwaterproofed, then for disposal, the article need only be broken toexpose its interior to the aqueous solvent and thereafter, dissolutionof the entire article will occur.

The waterproofing may be achieved in any suitable way or combination ofways, as will now be described.

(1) Polymer Crosslinking.

A thin layer of the surface of the article may be made water resistantby crosslinking the copolymer. One way of achieving this is to add anultra-violet sensitiser to the PVA during compounding, for examplesodium benzoate, benzamide, benzoic acid or tetrazolium salts. Afterforming an article from the plastics material, the article is subjectedto ultra-violet irradiation, during which the sensitiser promotescrosslinking of the polymer chains at the irradiated surface, renderingthe crosslinked polymers insoluble, with the effect that a thin layer ofthe PVA at the surface of the article becomes water resistant.Optionally, a migrating agent may be added to assist the movement of thesensitiser to the surface. Alternatively, the sensitiser may be appliedto the surface of the article after manufacture and prior toirradiation.

(2) Silanisation.

The article or a surface thereof may be coated with silane. The silanemay be in liquid or gaseous form. The article may be bathed in a silane,or the silane may be applied to the article by dipping, spraying orpainting. This is valid for light water resistance.

(3) Treatment With Other Waterproofing Compound.

A waterproofing compound may be added to the PVA feedstock duringcompounding of the plastics material. This compound may be a hydrophobicsubstance. A migrating agent may be added to assist movement of thewaterproofing compound to the surface of the article formed from theplastics material. The waterproofing agent may itself be a migratingagent. As an alternative to compounding the waterproofing agent into theplastics, it may be applied to the finished article by dipping, sprayingor painting. One suitable waterproofing agent is phenoxy resin.Polyvinylacetate or other suitable, non-toxic polymer may be used as asurface coat on the PVA article. To assist adhesion of the waterproofingagent to the surface of the article, it may be treated for example byelectrical treatment prior to coating to condition the surface so as torender it more able to accept and retain the waterproofing coating.

In some cases, it will be appropriate to manufacture the article fromhot soluble PVA. Provided that the article does not encounter water at atemperature in excess of about 45° C. during its normal use, such aproduct need not be surface water-proofed. After use, placing the objectin water heated to at least 50° C. will promote its dissolution fordisposal. An article prepared in this way will be fully or almost fullybiodegradable.

The invention will now be described more particularly with reference tothe following non-restrictive examples and to FIG. 1 of the drawings inwhich is shown an embodiment of the screw design used in the apparatusat the compounding stage of the process of the present invention.

EXAMPLE 1

Mixing Stage

A Prism lab 6 high speed mixer was used (Henschel 50 kg mixer alsoused).

Ingredients

5 kg PVA (degree of hydrolysis of 76.7 to 79.3 mol %)

0.25 kg stearamide (5% w/w of stearamide to weight of PVA)

0.25 kg of glycerol (5% w/w of glycerol to weight of PVA)

A high speed forced action blender was used. The PVA and stearamide wereadded to the mixer and mixed for 1 minute. The glycerol was added slowlyover a period of 30 seconds, with the mixer rotating at approximately500 rpm. As a result of the agitation, the mix became frothy ("fluffedup") and the mixer was stopped to push mixed material from the inside ofthe mixer. After 2-5 minutes, the mix had settled down and the mixer wasturned up to full speed, from 1,500 rpm to 3,000 rpm. As a result of thekinetic energy generated by the agitation of the mix, the temperatureincreased to 123° and went to 125° in 8 to 20 minutes depending on thetype of mixer used.

The temperature is a critical parameter to achieving high qualityproduct.

A vacuum was created at the top of the mixer to draw off any moisturevapour which had formed at the top of the mixer and which wouldotherwise condense back into the mix.

The mix was allowed to cool to 60-70° C. so that it was sufficientlycool to allow it to be bagged. The mix can be allowed to cool by itselfor optionally a heating/cooling jacket can be included on the mixervessel.

Alternatively mix can be transferred to another vessel to cool. Themixture was stirred occasionally to help cooling and break up any lumpswhich had formed. The product is in granular form and is bagged inair-tight bags.

Compounding/Pelleting Stage

A Prism TSE 16TC twin screw extruder with 41/2 mm die was used for thecompounding stage.

The temperature range was 200° C.-218° C. measured from the feed end ofthe screw to the die end.

The extruder is vented along the screw to allow moisture vapour to exitthe screw because otherwise bubbles occur in the strands. The productemerges from the extruder in the form of a strand which has elasticproperties. The strands must be dried in air using air knives, forinstance, and not in water. After cooling, the strands were cut intopellets using a Prism LPT 16 laboratory pelletiser. The pellets werethen bagged in an air tight fashion.

BRIEF DESCRIPTION OF DRAWING

The screw design of the twin screw extruder is shown in FIG. 1. A singlescrew apparatus could also be used for compounding.

Referring to FIG. 1, the screw is indicated generally by referencenumeral 1 and includes three zones, namely a feed zone 2, a work zone 3and a die zone 4.

The feed enters the screw through a feed port 5. Two other ports 6, 7are included along the length of the screw, to allow for addition ofmaterial if required, (6) and for venting (7) respectively. A heatingband and a temperature probe respectively are included at two locationsalong the length of the screw.

The configuration of the screw includes several elements namely anextrusion screw indicated by the letters EXT (length=1.5 times thediameter) and feedscrew elements indicated by the letters FS (lengthequal to its diameter). The screw also includes mixing elements(length=diameter divided by 4) which may be 0° offset, 90° offset or 15°offset. The mixing elements may be forwarding (F), reversing (R) oralternating (A).

Blowing Film

A Betol 0250 film tower machine was used.

The temperature profile along the screw extruder is as follows:

    ______________________________________                                        Feed zone of barrel                                                                           195-210° C.                                            Work zone of barrel                                                                           200-218° C.                                            Die zone        200-218° C.                                            ______________________________________                                    

Screens of 200/inch² gauge size are used to soften the memory of the PVAand reduce the risk of any possible extraneous matter and gels. Furtherscreens are also provided of 40/inch², 60/inch², 80/inch², 100/inch² and120/inch² secured to the 200/inch² screen to give it strength.

Screens are located between the end of the screw and the die.

Spraying the Waterproofing Agent, Phenoxy Resin, Onto the Film

Mixing (Before Spraying)

100 g phenoxy resin was mixed with 500 mls Methyl Ethyl Ketone (MEK)initially to 20% w/w solids. This is mixed in a high speed mixer or isleft to stand at a temperature of a minimum of 28° C. for 3-5 days withperiodic shaking to achieve a solution. When the phenoxy resin was insolution, a mixture comprising 500 mls of MEK and 12 mls water was addedto the solution. Thus the phenoxy resin was then in solution at aconcentration of approximately 10% w/w.

A 10% w/w solution of phenoxy resin was used for spraying a film ofthickness 40 μm. Alternatively 5% or 2.5% solution of phenoxy in MEKwith water added was also be used depending on the thickness of the filmto be sprayed. Lower concentrations of phenoxy resin in MEK with watermay also be used.

Spraying

Spraying was carried out in dry conditions and preferably at a minimumtemperature of 21° C. A Campbell Hausfeld Professional Turbo Spray (highvolume/low pressure finishing system HV2,000) was used for spraying butconventional sprayers may also be used. The humidity of the atmospherein which spraying is being conducted is a critical parameter. The filmwas sprayed so as to achieve good cover but without overspraying. Thinfilm below 40 μm needs stretching so that no folds occur during sprayingand must be held flat. Heavier plastics must also be held flat.Alternatively, heavier plastics (60 μm+) can be dipped or use sponge orroller to apply.

EXAMPLE 2

Mixing Stage

Ingredients

5 kg PVA (degree of Hydrolysis of 76.7 to 79.3 mol %)

0.5 kg glycerol (10% w/w) glycerol

0.25 kg (5% w/w) stearamide

The procedure is the same as in the mixing state described in Example 1.

Compounding/Pelletising Stage

The temperature profile along the screw extruder was as follows:

    ______________________________________                                        Feed zone of barrel                                                                           200° C.                                                Work zone of barrel                                                                           205° C.                                                Die zone        210° C.                                                Rpm 260                                                                       Output 2.5 kg/hr approximately                                                ______________________________________                                    

EXAMPLE 3

Mixing Stage

5 kgs PVA

0.75 kg glycerol (15% w/w) glycerol

0.25 kg (5% w/w) stearamide

Compounding/Pelletising Stage

    ______________________________________                                        Feed zone of barrel                                                                           200° C.                                                Work zone of barrel                                                                           215° C.                                                Die zone        216° C.                                                Rpm 260°                                                               Output 2.5 kg/hr approximately.                                               ______________________________________                                    

Further Examples of Parameters at the Compounding and Blowing Stages

A Prism TSE 16TC apparatus was used for compounding with a blow lineattachment for blowing film.

The temperature of the various zones is given in °C. in the followingexamples.

EXAMPLE 4

    ______________________________________                                        Film        Die          Work   Feed                                          Blowing Zone                                                                              Zone         Zone   Zone                                          ______________________________________                                        215         209          207    200                                           ______________________________________                                         Good quality film was produced.                                          

EXAMPLE 5

    ______________________________________                                        Film        Die          Work   Feed                                          Blowing Zone                                                                              Zone         Zone   Zone                                          ______________________________________                                        215         209          209    197                                           ______________________________________                                        Pressure       40-45 bar (4000-4500 kN/M.sup.2)                                              (pressure at exit end of screw)                                Feed           0.5                                                            rpm            303                                                            ______________________________________                                    

EXAMPLE 6

    ______________________________________                                        Film        Die          Work   Feed                                          Blowing Zone                                                                              Zone         Zone   Zone                                          ______________________________________                                        215         212          209    199                                           ______________________________________                                        Pressure       40-45 bar (4000-4500 kN/M.sup.2)                               Torque         7.8-8.0 NM                                                     Rpm            301                                                            ______________________________________                                    

EXAMPLE 7

    ______________________________________                                        Film        Die          Work   Feed                                          Blowing Zone                                                                              Zone         Zone   Zone                                          ______________________________________                                        195         202          191    183                                           ______________________________________                                        Pressure         60 bar (6000 kN/M.sup.2)                                     Torque           8.0-8.4 NM                                                   ______________________________________                                         These parameters resulted in poor quality film.                          

EXAMPLE 8

    ______________________________________                                        Film        Die          Work   Feed                                          Blowing Zone                                                                              Zone         Zone   Zone                                          ______________________________________                                        188         201          188    182                                           ______________________________________                                        Pressure         75 bar (7500 kN/M.sup.2)                                     Torque           8.6 NM                                                       ______________________________________                                         These parameters also resulted in production of poor quality film.       

EXAMPLE 9

    ______________________________________                                        Film        Die          Work   Feed                                          Blowing Zone                                                                              Zone         Zone   Zone                                          ______________________________________                                        182         202          189    182                                           ______________________________________                                         These parameters resulted in the production of poor quality film.        

EXAMPLE 10

    ______________________________________                                        Film        Die          Work   Feed                                          Blowing Zone                                                                              Zone         Zone   Zone                                          ______________________________________                                        192         197          181    176                                           ______________________________________                                         These parameters also resulted in production of poor quality film.       

EXAMPLE 11

    ______________________________________                                        Film        Die          Work   Feed                                          Blowing Zone                                                                              Zone         Zone   Zone                                          ______________________________________                                        192         191          177    171                                           ______________________________________                                         It was not possible to produce film at these temperatures.               

EXAMPLE 12

    ______________________________________                                        Film        Die          Work   Feed                                          Blowing Zone                                                                              Zone         Zone   Zone                                          ______________________________________                                        213         212          208    200                                           ______________________________________                                        Pressure         45 bar (4500 kN/M.sup.2)                                     Rpm              301                                                          ______________________________________                                         Good quality film was produced.                                          

EXAMPLE 13

    ______________________________________                                        Film        Die          Work   Feed                                          Blowing Zone                                                                              Zone         Zone   Zone                                          ______________________________________                                        214         211          207    200                                           ______________________________________                                        Pressure       40-45 bar (4000-4500 kN/M.sup.2)                               Torque         8-8.5 NM                                                       Feed           0.35                                                           ______________________________________                                    

EXAMPLE 14

    ______________________________________                                        Film        Die          Work   Feed                                          Blowing Zone                                                                              Zone         Zone   Zone                                          ______________________________________                                        219         214          215    202                                           ______________________________________                                         Good quality film was produced.                                          

EXAMPLE 15

    ______________________________________                                        Film        Die          Work   Feed                                          Blowing Zone                                                                              Zone         Zone   Zone                                          ______________________________________                                        222         218          216    203                                           ______________________________________                                         Good quality film was produced.                                          

EXAMPLE 16

    ______________________________________                                        Film        Die          Work   Feed                                          Blowing Zone                                                                              Zone         Zone   Zone                                          ______________________________________                                        225         220          219    204                                           ______________________________________                                         These parameters resulted in borderline quality.                         

EXAMPLE 17

    ______________________________________                                        Film        Die          Work   Feed                                          Blowing Zone                                                                              Zone         Zone   Zone                                          ______________________________________                                        229         221          221    204                                           ______________________________________                                         Poor quality film was produced.                                          

EXAMPLE 18

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        228        223          224    205                                            ______________________________________                                         Poor quality film was produced.                                          

EXAMPLE 19

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        228        226          227    206                                            ______________________________________                                         Poor quality film was produced.                                          

EXAMPLE 20

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        228        229          231    206                                            ______________________________________                                         Poor quality film was produced.                                          

EXAMPLE 21

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        228        231          231    206                                            ______________________________________                                         Poor quality film was produced.                                          

EXAMPLE 22

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        238        230          231    206                                            ______________________________________                                         It was not possible to blow film from the material exiting the screw          extruder at these temperatures.                                          

EXAMPLE 23

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        213        210          207    201                                            ______________________________________                                         Good quality film was produced.                                          

    ______________________________________                                        Pressure       35-40 bar (3500-4000 kN/M.sup.2)                               Torque         7.6-8.0 NM                                                     Rpm            302                                                            ______________________________________                                    

EXAMPLE 24

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        212        211          208    201                                            ______________________________________                                         Good quality film was produced.                                          

EXAMPLE 25

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        213        210          204    194                                            ______________________________________                                         Good quality film was produced.                                          

    ______________________________________                                        Pressure       40-45 bar (4000-4500 kN/M.sup.2)                               Torque         7.7-8.2 NM                                                     ______________________________________                                    

EXAMPLE 26

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        213        209          208    194                                            ______________________________________                                    

EXAMPLE 27

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        210        208          202    194                                            ______________________________________                                    

EXAMPLE 28

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        209        210          204    197                                            ______________________________________                                    

EXAMPLE 29

Ingredients

5 kg PVA

5% w/w stearamide (0.25 kg)

5% w/w glycerol (0.25 kg)

Temperatures

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        211        211          207    202                                            ______________________________________                                         The quality of the film produced was good                                

    ______________________________________                                        Pressure       35-40 bar (3500-4000 kN/M.sup.2)                               Torque         7.9-8.2 NM                                                     RPM            303                                                            ______________________________________                                    

EXAMPLE 30

Ingredients

5 kg PVA

4% w/w stearamide (0.20 kg)

5% w/w glycerol (0.25 kg)

Temperatues

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        212        210          207    202                                            ______________________________________                                         The quality was poor and the film produced was not commercial quality.   

    ______________________________________                                        Pressure       45-50 bar (4500-5000 kN/M.sup.2)                               Torque         8-8.3 NM                                                       RPM            301                                                            ______________________________________                                    

EXAMPLE 31

Ingredients

5 kg PVA

3% w/w stearamide (0.15 kg)

5% w/w glycerol (0.25 kg)

Temperatures

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        212        210          208    202                                            ______________________________________                                         The film was poor quality.                                               

    ______________________________________                                        Pressure       48-50 bar (4800-5000 kN/M.sup.2)                               Torque         8.3-8.5 NM                                                     RPM            303                                                            ______________________________________                                    

EXAMPLE 32

Ingredients

5 kg PVA

2% w/w stearamide (0.10 kg)

5% w/w glycerol (0.25 kg)

Temperatures

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        212        212          209    202                                            ______________________________________                                         The film produced was poor quality.                                      

    ______________________________________                                        Pressure       58-60 bar (5800-6000 kN/M.sup.2)                               Torque         9.1-9.4 NM                                                     RPM            303                                                            ______________________________________                                    

EXAMPLE 33

Ingredients

5 kg PVA

1% w/w stearamide (0.05 kg)

5% w/w glycerol (0.25 kg)

Temperatures

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        212        215          210    202                                            ______________________________________                                         The quality produced was poor.                                           

    ______________________________________                                        Pressure       60-64 bar (6000-6400 kN/M.sup.2)                               Torque         9.7-10.4 NM                                                    RPM            303                                                            ______________________________________                                    

EXAMPLE 34

Ingredients

5 kg PVA

7.5% w/w stearamide (0.375 kg)

Temperatures

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        212        209          201    198                                            ______________________________________                                         Very poor quality film produced.                                         

    ______________________________________                                        Pressure       40 bar (4000 kN/M.sup.2)                                       Torque         7.1-7.4 NM                                                     ______________________________________                                    

EXAMPLE 35

Ingredients

5 kg PVA

5% w/w stearamide (0.25 kg)

4% w/w glycerol (0.20 kg)

Temperatures

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        214        219          211    199                                            ______________________________________                                         The quality of the film produced was good.                               

    ______________________________________                                        Torque         9.5-9.9 NM                                                     ______________________________________                                    

EXAMPLE 36

Ingredients

5 kg PVA

5% w/w stearamide (0.25 kg)

3% w/w glycerol (0.15 kg)

The quality of the film produced was poor.

EXAMPLE 37

Ingredients

5 kg PVA

5% w/w stearamide (0.25 kg)

2% w/w glycerol (0.10 kg)

Very poor quality film produced.

The following examples detail the compounding temperatures resultingfrom processing the material under various different conditions at thepre-mixing stages.

EXAMPLE 38

The PVA/stearamide and glycerol were heated to 140° C. in the forcedaction blender.

Temperatures at Compounding Stage

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        214        212          210    197                                            ______________________________________                                         The quality of the film produced was good.                               

    ______________________________________                                        Pressure       50-55 bar (5000-5500 kN/M.sup.2)                               Torque         8.1-8.6 NM                                                     ______________________________________                                    

EXAMPLE 39

The mix was heated to 145° C. during the pre-mix stage.

Temperatures at Compounding Stage

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        213        213          211    197                                            ______________________________________                                         The quality was borderline acceptable.                                   

    ______________________________________                                        Pressure       65 bar (6500 kN/M.sup.2)                                       Torque         6.6-6.9 NM                                                     ______________________________________                                    

EXAMPLE 40

The mix was heated to 150° C. during the pre-mix stage.

Temperatures at Compounding Stage

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        215        214          211    197                                            ______________________________________                                         The quality was borderline acceptable.                                   

    ______________________________________                                        Pressure       65 bar (4000 kN/M.sup.2)                                       Torque         8.6-8.9 NM                                                     ______________________________________                                    

EXAMPLE 41

The mix was heated to 160° C. during the pre-mix stage.

Temperatures at Compounding Stage

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        213        209          210    198                                            ______________________________________                                         These parameters produced poor quality film.                             

    ______________________________________                                        Pressure       40 bar (4000 kN/M.sup.2)                                       Torque         7.1-7.3 NM                                                     ______________________________________                                    

EXAMPLE 42

The mix was heated to 119° C. during the pre-mix stage.

Temperatures at Compounding Stage

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        214        215          211    197                                            ______________________________________                                         The quality of the film produced was good.                               

    ______________________________________                                        Pressure       70 bar (7000 kN/M.sup.2)                                       Torque         9.0-9.4 NM                                                     ______________________________________                                    

EXAMPLE 43

The mix was heated to 117° C. during the pre-mix stage.

Temperatures at Compounding Stage

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        216        215          211    197                                            ______________________________________                                         The quality of the film produced was good.                               

    ______________________________________                                        Pressure       68-70 bar (6800-7000 kN/M.sup.2)                               Torque         8.7-9.0 NM                                                     ______________________________________                                    

EXAMPLE 44

The mix was heated to 113° C. during the pre-mix stage.

Temperatures at Compounding Stage

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        213        215          211    196                                            ______________________________________                                         The quality of the film produced was good.                               

    ______________________________________                                        Pressure       70-75 bar (7000-7500 kN/M.sup.2)                               Torque         9.2-9.6 NM                                                     ______________________________________                                    

EXAMPLE 45

The mix was heated to 106° C. during the pre-mix stage.

Temperatures at Compounding Stage

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        214        217          212    196                                            ______________________________________                                         The quality of the film produced was good.                               

    ______________________________________                                        Pressure       75-80 bar (7500-8000 kN/M.sup.2)                               Torque         9.6-10.0 NM                                                    ______________________________________                                    

EXAMPLE 46

The mix was heated to 100° C. during the pre-mix stage.

Temperatures at Compounding Stage

    ______________________________________                                        Film                                                                          Blowing    Die          Work   Feed                                           Zone       Zone         Zone   Zone                                           ______________________________________                                        213        213          209    195                                            ______________________________________                                         The quality of the film produced was not commercial quality.             

    ______________________________________                                        Pressure       70-80 bar (7000-8000 kN/M.sup.2)                               Torque         8.1-8.4 NM                                                     ______________________________________                                    

The improvements to biodegradable PVA plastics materials describedherein can be summarised as follows:

1. The PVA an be readily formed and worked to produce a non-laminatedlayer of PVA as a film or a shaped article.

2. Any or each surface of the film or article may be treated to renderit water resistant.

3. This PVA plastics product, when ruptured and/or immersed in waterwill dissolve completely and will biodegrade to completion over a periodof about 28 days excluding the phenoxy resin waterproofing agent whichdoes not biodegrade.

4. All the components used in the manufacture of the PVA are foodgradeadditives.

It will of course be understood that the invention is not limited to thespecific details described herein, which are given by way of exampleonly, and that various modifications and alterations are possible withinthe scope of the appended claims.

I claim:
 1. A method of manufacturing a biodegradable plastics materialcomprising the steps of mixing partially hydrolysed, water solublepolyvinyl alcohol (PVA) co-polymer feedstock with a stabiliser, adding aplasticiser to the mixture of stabiliser and PVA and mixing at atemperature in the range of 106 to 140° C., and compounding theresultant material at a temperature in the range of 195-225° C. toproduce a useable, commercial product which can readily be worked byknown processes and is suitable for the manufacture of water soluble andbiodegradable articles, the stabiliser comprising stearamide or stearateused in an amount in the range of 4 to 6% weight/weight PVA.
 2. Themethod according to claim 1, wherein the mixing of the PVA, stabiliserand plasticiser is carried out at a temperature in the range of 116 to135° C.
 3. The method according to claim 1, wherein the mixing of thePVA, stabiliser and plasticiser is carried out at a temperature in therange of 123 to 129° C.
 4. The method according to claim 1, wherein theplasticiser comprises glycerol or glycerine solution or soya bean oil.5. The method according to claim 1, wherein the plasticiser is includedin an amount in the range of 3 to 15% weight/weight PVA.
 6. The methodaccording to claim 1, wherein the PVA, stabiliser and plasticiser aremixed in a forced action blender.
 7. A method according to claim 1,including the step of pelletising the resultant product to produce auseable, commercial pellet.
 8. The method according to claim 1, whereinthe method further includes the step of processing the compoundedproduct or pellet further by blow moulding, cast extrusion, injectionmoulding or any other suitable plastics processing procedure to producean article.
 9. The method according to claim 8, further comprising thestep of applying a waterproofing agent to at least a portion of thesurface of the article so that at least a portion thereof is renderedresistant to water to prevent premature dissolution of the article oncontact with water.
 10. The method according to claim 9, wherein thewaterproofing agent is a phenoxy resin.
 11. The method according toclaim 1, wherein the PVA feedback comprises cold or hot soluble,partially hydrolysed PVA which is 70-85 wt % polyvinyl alcohol.
 12. Abiodegradable, plastics material produced by a method as claimed inclaim
 1. 13. An article produced by the method as claimed in claim 1,wherein the article is fully or substantially fully biodegradable. 14.An article produced by the method as claimed in claim 1, wherein thebiodegrading of the article commences on contact of the article withwater.